1. Field of the Invention
The invention relates to a method for producing a casting mold from a composite mold material for foundry purposes, that is composed of various types of mold materials that are heat-resistant for casting metals and that have a differing substantive composition or a differing content of organic or inorganic binders. Such mold materials in particular are combinations of heat-resistant molding compositions and core compositions that consist of a refractory inorganic base material, usually quartz sand, and a binder system. For special demands on the mold and on the casting, refractory ceramic compositions and materials are also used that can be machined by cutting production processes. Because of its desirable price, its abundance, and its properties, quartz sand is the predominant mold base material.
2. The Prior Art
It has long been known in practice, in the search for economical methods in the production of casting molds, how to use mold materials with different properties and accordingly of various compositions. According to Ambos, Urformtechnik metallischer Werkstoffe [Pattern Engineering of Metallic Materials], Verlag für Grundstoffindustrie, 2nd Edition, Leipzig 1982, page 51, it is customary in the manual and mechanized production of molds and cores, whenever these exceed a given minimum size, to apply a thin layer of heavy-duty mold material to the pattern or to the core box wall. This mold material comes into direct contact with the liquid metal during the casting and must have properties adequate for the casting. Therefore, it contains a relatively high proportion of binder and is called a pattern mold material.
Most of the mold box or core box, however, is filled with a mold material of lower quality, the so-called filling mold material or filling sand. It contains substantially less binder and provides corresponding cost reductions compared with filling the entire mold with heavy-duty mold material like that needed at the contact surface of the mold material with the liquid metal. It is a drawback that a pattern is needed for producing a casting mold. The production of a pattern is associated with a further cost increase and a considerable expenditure of time. The method is also restricted to the production of casting molds that consist exclusively of foundry mold sand.
Japanese Patent No. JP 61 245 942 A1 discloses a method for producing a lost-wax casting mold made of a composite mold material that has a plaster mold embedded in a sand mold. To make the plaster mold and the sand mold, a pattern has to be prepared each time. For the plaster mold, a wax pattern is made that is placed in a container and a plaster slurry is poured over it. The plaster mold is subjected to primary and secondary calcinations so that the ceramic mold is hardened. The plaster mold is embedded in the casting mold with foundry mold sand and the liquid metal is then poured in. Various time-consuming production steps are necessary with this method to produce the pattern for the sand mold and the plaster mold, which are associated with substantial costs. For this reason the proposed method is not suitable in particular for the fast production of prototypes.
Economical and fast prototypes increasingly approximating design studies and functional purposes are needed in product development in order to reduce high development costs. The fast availability of prototypes is not provided for because of the necessary production of patterns, because the production of ceramic casting molds requires a lot of time.